The present invention relates to a lighting control apparatus for signals such as flashers, brake lights and the like which are mounted on vehicles so as to be displayed to inform a driver when one of the signals is malfunctioning.
Vehicles have a variety of flasher lights or blinkers for indicating to a third party when a driver wants to make a right or left turn. Vehicles also have brake lights for signalling to a third party that the driver is applying the brakes and so is about to slow down or stop.
These signals such as flashers and brake lights are designed to indicate the driving state of the vehicle, and it is important for safe driving that all the lights be free from disconnection and function properly. For this reason, when a malfunction such as disconnection of the lamps occurs, various signalling means for quickly alerting a driver have been developed.
For example, a resistor element for detecting a value of an ON current is connected in series to a circuit of the ON current supplied to the signal lights, and a voltage generated across the two ends of this resistor element is detected so as to determine the value of the ON current. When a decrease in the ON current is detected, it is determined that at least one of a plurality of signal lights is disconnected.
In such a means for detecting the disconnection of a signal light, the resistance of the resistor element in which the ON current flows must correspond to a reference level set at a discrimination circuit which detects changes in the voltage generated in the resistor's element portion.
The discrimination circuit comprises a reference voltage setting circuit, in which at least two resistor elements are connected in series for setting the voltage of a connecting point of these two resistor elements as a reference voltage, and a comparator for comparing the reference voltage and a voltage signal generated in a resistor element portion to which the ON current is supplied. Therefore, in order to reliably detect the disconnection of the signals in this circuit, the voltage generated in the resistor element portion must be properly set with respect to the reference voltage. For this reason, the detecting resistor circuit and the resistor circuit for setting the reference voltage should respectively comprise a combination of a plurality of resistor elements or a variable resistor element.
However, since the resistor elements constituting the detecting resistor circuit are connected to the discrimination circuit by, for example, welding, it is difficult to set a specific resistance at a connecting portion of the detecting resistor elements. Therefore, when such a control apparatus for signal lights is designed, the resistances of the resistor elements must be adjusted so as to match the value of the reference voltage which is set in the discrimination circuit after connecting the detecting resistor elements to a circuit board comprising the discrimination circuit.